test-bot: fix undefined method error

The method `fix_encoding!` is private to `Homebrew::Step` but is also
required by the `Homebrew.sanitize_output_for_xml` method for truncating
overly long logs. Move `fix_encoding!` into the `Homebrew` module to
make it accessible from both this method and the `Homebrew::Step` class.

This amends commit 343091c8.

Library/Homebrew/cmd/test-bot.rb

@@ -43,6 +43,24 @@ module Homebrew
     String.method_defined?(:force_encoding)
   end
 
+  if ruby_has_encoding?
+    def fix_encoding!(str)
+      # Assume we are starting from a "mostly" UTF-8 string
+      str.force_encoding(Encoding::UTF_8)
+      return str if str.valid_encoding?
+      str.encode!(Encoding::UTF_16, :invalid => :replace)
+      str.encode!(Encoding::UTF_8)
+    end
+  elsif require "iconv"
+    def fix_encoding!(str)
+      Iconv.conv("UTF-8//IGNORE", "UTF-8", str)
+    end
+  else
+    def fix_encoding!(str)
+      str
+    end
+  end
+
   def resolve_test_tap
     if tap = ARGV.value("tap")
       return Tap.fetch(tap)
@@ -188,26 +206,6 @@ module Homebrew
 
       exit 1 if ARGV.include?("--fail-fast") && failed?
     end
-
-    private
-
-    if Homebrew.ruby_has_encoding?
-      def fix_encoding!(str)
-        # Assume we are starting from a "mostly" UTF-8 string
-        str.force_encoding(Encoding::UTF_8)
-        return str if str.valid_encoding?
-        str.encode!(Encoding::UTF_16, :invalid => :replace)
-        str.encode!(Encoding::UTF_8)
-      end
-    elsif require "iconv"
-      def fix_encoding!(str)
-        Iconv.conv("UTF-8//IGNORE", "UTF-8", str)
-      end
-    else
-      def fix_encoding!(str)
-        str
-      end
-    end
   end
 
   class Test